Typically, in the building or maintenance of roads, a vehicle containing materials such as sand, gravel, tarmac or road stone is driven to a site and the vehicle bed is tipped either to one side or to the rear to dump the material. The material must then be manually spread evenly over the site as required. Often, when the bed is tipped to the side, the vehicle will become trapped by the tipped material and can only be freed once the work force has cleared the material away from the vehicle's wheels. Whilst it is possible to drive the vehicle forwards while tipping to the rear this operation can be dangerous as the vehicle bed may unload unevenly. This may occur when some of the material freezes overnight and becomes stuck to the bottom of the bed, which in extreme circumstances can cause the vehicle to overturn whilst tipping.
Other systems exist in which one or more conveyors are mounted in the floor of a vehicle bed which allows the material to be discharged whilst the vehicle is driven forward. However, the costs of fitting such a system to a vehicle are prohibitive. Such systems are especially susceptible to mechanical breakdown when larger pieces of material jam the conveyor which can result in the bed unloading unevenly and so adversely affecting the stability of the whole vehicle.